This invention relates to aquaculture of marine worms and particularly although not exclusively methods for controlling growth of marine worms.
Marine bait worms are animals in the Class Polychaeta of the Phylum Annelida or in the Phylum Sipunculida or are such other animals as may be generally referred to as worms which may be used as bait by anglers. Such worms are also used as feedstuffs for fish, crustaceans and other organisms, for toxicity testing and for other scientific purposes.
Naturally occurring supplies of marine worms are not inexhaustible and collection of marine worms has been recognised as a cause of serious environmental concern.
Aquaculture of marine worms provides a sustainable source. However, the seasonal breeding cycle of marine worms hinders provision of a constant supply of worms throughout the year. Since the natural fecundity of female marine worms is very high, large numbers of fertilised eggs are available from time to time that are surplus to requirements and are usually wasted. The use of cryopreservation techniques and other methods for the preservation of larvae may provide effective supplies of juveniles throughout the year.
A further constraint and hindrance to the maximum production of worms throughout the year is the seasonal variation of growth rate that may occur in cultured marine worms and which may be related to the onset of sexual development or may be observed to occur even in the absence of signs of sexual maturation.
According to a first aspect, the present invention provides a method of controlling the growth of polychaete worms as recited in claim 1.
The quality, quantity and/or duration of the light may be controlled in the method.
Preferred features which may be used with aspects of the invention are set out in the dependent Claims.
The worms are preferably maintained in a controlled temperature regime, and may have an effective date of birth other than during the natural breeding season. The worms can be recovered from a preservation system, such as a cryopreservation system.
The worms are preferably induced to breed outside the normal breeding season as well as within the normal breeding season.
Preferably, the photoperiodic regime to which the worms are subjected is substantially equivalent to the natural photoperiodic regime and optionally comprises one or more periods of light and one or more periods of dark within a 24 hour or near to 24 hour day. The duration of the periods of light and the periods of dark may be controlled and changed from day to day as required.
The photoperiodic regime may be one that is substantially equivalent to the natural photoperiodic regime but is displaced in time (eg by three to six months) relative to the natural photoperiodic regime.
The photoperiodic regime may comprise periods of time when the duration of light in the 24 hour or near to 24 hour photoperiodic day is held constant and in which the duration of light is greater than 12 hours.
The period of natural daylight may be supplemented by artificial lights during a period prior to dawn and or after dark.
The photoperiodic regime may be one in which natural daylight is excluded and light is provided entirely by artificial lights, the duration of lighting being adjusted such that the total duration of light is greater than 12 hours in any one 24 hour or near to 24 hour period.
The photoperiodic regime may be one in which short periods of light are given at regular intervals to simulate a fixed pattern of light and dark by means of a skeleton photoperiod.
The photoperiodic regime may be one in which a short exposure to light occurs shortly or some hours after the transition to dark having the effect of resetting the time at which the dusk light dark transition is effective.
The photoperiodic regime may be one in which a short exposure to light occurs shortly before, or some hours before, the transition to light having the effect of resetting the time at which the dawn dark light transition is effective.
The duration of the period of short days or the duration of the period of long days can be varied. The photophase may be kept substantially constant during a period of short days, or a period of long days.
The worms can be members of the order Phyllodocida e.g. the Nereidae family, and especially the species Nereis (Neanthes) virens. 
Alternatively the worms are members of the order of Eunicide, e.g. family Eunicidae genus Marphysa and/or the family Onuphidae genus Diapatra.
The invention advantageously results in increased rate of weight gain and/or increased segment proliferation/regeneration rate and/or increased rate of feeding and/or activity during periods when the naturally occurring duration of light is such that the rate of weight gain and/or increased segment proliferation/regeneration rate and/or increased rate of feeding and activity is lower than the optimum rate that can be achieved.
Exposure of the worms to light regimes in which the duration of continuous light or the interval between the period of light interpreted as dawn and the period of light interpreted as dusk is greater than the critical value below which the growth rate and/or regeneration rate and/or feeding rate and/or activity rate is reduced can result in an increased growth rate and/or regeneration rate and/or feeding rate and/or activity rate.
In the example of the ragworm Nereis virens the advantageous results that can be achieved by the application to the invention will normally be maximally achieved during periods when the duration of light in the photoperiodic day is 12 hours of light or less.
In the example of the ragworm Nereis virens the advantageous results that can be achieved by the application of the invention will be achieved to a lesser though commercially significant degree during periods when the duration of light in the photoperiodic day is between 12 hours and 16 hours of light.
In the example of the ragworm Nereis virens the advantageous results that can be achieved by the application of the invention may be achieved at any time be exposure of animals to photoperiodic conditions in which the duration of the light is greater than 16 hours of light in a 24 hour period.
In the example of the ragworm Nereis virens exposure of the worms to any light regime in which the duration of continuous light, or the interval between the period of light interpreted as dawn and the period of light interpreted as dusk, is greater than the critical value of 12 hours of light per 24 hour day during periods when the photoperiod is naturally less than 12 hours per day can result in an increased growth rate and/or regeneration rate and/or feeding rate and/or activity rate to the advantage of the producer. The degree of advantage can be dependent on the natural duration of the period of light at the time of application of the invention and on the duration of the artificial exposure to light or the duration of the effective duration of the light as achieved by the application of a skeleton photoperiod or the extension of the effective duration of the period of light by the exposure of the animals to short periods of light before dawn or after dusk.
Certain embodiments of the invention permit the producer of worms to maintain the rates of growth and/or regeneration and/or segment proliferation and/or feeding and/or activity of the worms to be maintained at a high level at all seasons of the year and in all stocks whatever the actual date of birth and/or recovery from a preservation system subject only to the normal constraints of the temperature regime and/or feeding regime to which the animals are subjected.
Long day treatments can induce greater growth in terms of weight gain, segment proliferation and/or regeneration of truncated worms.
In order to facilitate description the following terms are defined:
Photoperiodic Day
the duration of a single sequence of light and dark usually with a total duration close to 24 hours. The relative duration of the periods of light and dark in the 24 hour photoperiodic day may be described as LD x:y where x is the duration of light and y is the duration of dark. Thus a 24 hour photoperiodic day LD 8:16 is a sequence of 8 hours of light and 16 hours of dark and a 24 hour photoperiodic day LD 16:8 is a sequence of 16 hours light and 8 hours dark, each repeated every 24 hours.
The period of light in the LD cycle may be referred to as the Photophase.
The period of dark in the LD cycle may be referred to as the scotophase.
Natural Photoperiodic Regime
the annual sequence of photoperiodic days that occurs naturally at the location at which the animals are kept or the work is being carried out;
Effective Date of Birth
the actual date of fertilisation of an animal or the date of recovery of the animal from a preservation system;
Photophase
the duration of a period of light in the photoperiodic day;
Scotophase
the duration of dark in the photoperiadic day;
Critical Photophase
the duration of a photophase which is such that any greater photophase will be interpreted as being a long day and which is such that any shorter photophase is interpreted as a short day and which, in the specific case of the reaction of Nereis (Neanthes) virens described herein is a photophase of between 12-13 hours in a 24 hour day;
Short Day
a 24 hour photoperiodic day in which the photophase is substantially less than the critical photophase length ie 12 hours or less for Nereis (Neanthes) virens for growth of eggs;
Long Day
a 24 hour photoperiodic day in which the photophase is substantially greater than the critical photophase ie 13 or more hours for Nereis (Neanthes) virens for growth of eggs;
Optionally, the photophase is controlled. In an embodiment of the invention the photophase can be varied (ie increased) to control the growth while the scotophase can be maintained constant. Alternatively, the scotophase can be varied (ie deceased) while the photophase remains constant. Alternatively, the photophase and scotophase can both be varied. The photoperiod can be 24 h or some other advantageous period.
In an embodiment of the invention the duration of the photophase in a 24 hour LD cycle is maintained above 12 hours light and the duration of the scotophase is correspondingly less than 12 hours darkness. The duration of the photophase is preferably 13 hours of light or substantially greater than 13 hours of light. The total duration of the photophase and of the scotophase may be constant each day or alternatively may be allowed to vary progressively as occurs naturally between the spring and autumn equinox in the Northern hemisphere.
The photoperiodic day may be 24 hours or some other period close to 24 hours or my be a period that is a multiple of 24 hours such as 48 hours or 72 hours.
An embodiment of the invention will now be described by way of example and without limitation.